I have a 55 with a severe leak from the torque ballretainer. Is it possible to replace the rear seals without removing the transmission from the car???

As far as I'm aware, you only (!) have to remove the diff and torque tube assembly.

I've got the same problem on my '57 where it leaks mainly in D or L. I've yet to tackle the problem, as I know it's a big job and I'm not sure if I'll re-seal the whole trans in the process ($). I've got a shop manual, so I guess I'll start reading for both of us...

If the torque ball is the problem, you can replace the seal without removing the trans. You just have to pull the rear end back far enough to get the driveshaft loose .You can then replace the seal and reassemble the unit.